This invention is directed to tube bending machines and, more particularly, to control systems for tube bending machines.
Originally, tubes were bent with hand-operated bending machines on a trial-and-error basis until they matched preexisting samples or layouts, or until they fit the requirements of a particular assembly of tubes. Later, measuring devices such as tapes, scales and protractors, were added to the bending machines to assist an operator in reproducing a tube configuration once its bending coordinates were established. However, such machines were found to be difficult and tedious to operate. As a result, still later, powered bending machines with systems of mechanical stops were devised. The use of mechanical stops made it possible for the operator to set-up stop points at various linear and rotational tube coordinates, in sequence. The tube was then mounted in the machine and sequentially moved to the positions defined by the stops. Such bending machines resulted in substantially identical tubes being bent in a rapid manner, once the stops were setup and verified. However, while substantially identical, the tubes were not exactly identical due to the coarseness of the stop indexing scales. The accuracy of the distance between succeeding bend tangents was usually in the order of plus or minus 1/16th to 1/8th inch and the accuracy of the rotational angle between bends was usually in the order of plus or minus 1/2 to 1.degree., depending on the size and complexity of the equipment. Moreover, the number of mechanical stops that can be set up is low; hence the number of bends that can be made without setting up a new set of stops is low.
More recently, fully automatic numerical control (NC) systems for controlling tube bending machines have been developed. Fully automatic NC systems digitally control the bending coordinates of power tube positioning systems according to a preestablished program contained on tape, punchcards or in a computer-type memory and have distance between bend accuracies of plus or minus 0.01 inch and angle between bend accuracies of plus or minus 0.1 degree.
While fully automatic NC tube bending machines have a substantial number of advantages over prior art machines using mechanical stops, they also have several disadvantages. Specifically, fully automatic NC equipment is relatively expensive, particularly when the power positioning equipment must operate over long (up to 40 feet) bed lengths. In addition, they are relatively insensitive to tube support requirements. Such support requirements are particularly critical when the last bends of a long tube are being formed, because the inertia of a long length of previously formed tube cantilevered forward of the bending head can cause the tube to be severely distorted through whipping action if the bend motion is too fast. A further disadvantage of fully automatic NC tube bending machines is the fairly large space envelope that must be evacuated by the operator once a bending cycle is initiated. The space envelope is, of course, determined by the tube gyrations that occur as a tube is being bent.
Therefore, it is an object of this invention to provide a new and improved control system for tube bending machines.
It is also an object of this invention to provide a control system for tube bending machines that is substantially lower in cost than fully automatic NC tube bending machines that include power positioning equipment, yet provides bending accuracy substantially equivalent to the bending accuracy of such machines.
It is another object of this invention to provide a semiautomatic control system for tube bending machines.
It is yet another object of this invention to provide a semiautomatic control system for tube bending machines that displays bend position data and actual tube position data such that an operator can quickly and accurately determine if a tube is appropriately positioned prior to being bent.